MANILA (Reuters) -Regular power supply has been restored at the main Philippine airport's Terminal 3, the airport authority said on Monday, after an almost nine-hour outage led to the cancellation of 48 Cebu Pacific domestic flights.

Cebu Pacific also confirmed that electricity had been restored at the Ninoy Aquino International Airport Terminal 3, in a notice on its Facebook page. Only Cebu Pacific flights to and from the capital Manila were affected.

Emergency power backup enabled critical facilities at the terminal, such as airline and immigration computers to function partially during the outage, which came as many Filipinos were returning home from a three-day weekend.

Cebu Pacific offered its passengers departing to and from Terminal 3 an option to rebook or to request refunds to be put in a travel fund for future use.

The outage, initially blamed by some airport engineers on a "fault current" affecting the electrical system, caused congestion at check-in counters and stranded passengers, some of them expressing dismay and frustration on social media.

Transportation Secretary Jaime Bautista said authorities will look into the cause of the outage. In a media briefing, he said he was not discounting the possibility of sabotage.

The outage came about four months after Philippine authorities halted hundreds of flights as they shut down the country's airspace on New Year's Day, also due to a power outage that caused the air traffic control in Manila to malfunction.

Six of the Southeast Asian nation's largest conglomerates have made a fresh 100 billion peso ($1.79 billion) bid to the government to upgrade and operate the ageing gateway, which has been ranked among the world's worst travel hubs due to regular flight delays and outdated facilities.

(Reporting by Akanksha Khushi in Bengaluru and Enrico Dela Cruz in Manila; Editing by Christian Schmollinger, Kenneth Maxwell and Sharon Singleton)